1. Field of the Invention
Aspects of the present invention relate to a secondary battery, and more particularly, to a Positive Temperature Coefficient (PTC) device, a Protective Circuit Module (PCM) including the PTC device, and a secondary battery including the Protective Circuit Module (PCM).
2. Description of the Related Art
Among the types of prismatic secondary batteries, a bare cell generally comprises a can, electrode assemblies stored in the can, and a cap assembly connected to the can. Safety devices such as Positive Temperature Coefficient (PTC) devices and thermal fuses are installed outside bare cells. Each safety device is connected to at least one electrode terminal of a bare cell and the device blocks current from flowing outside the bare cell when the battery temperature rises, or the battery voltage falls below or rises above a reference voltage because of excessive charge and discharge. PTC devices prevent batteries from damage and deterioration.
PTC devices have recently been installed in Protective Circuit Modules (PCM's). Solder-based surface mount technologies can be used in order to mount the PTC device. For example, in a Protective Circuit Module (PCM) in which an electrical terminal having a conductive layer is exposed, the terminal of a PTC device is disposed on the electrical terminal having a conductive layer. The Protective Circuit Module (PCM) passes through a high temperature region. The conductive layer on the surface of the electrical terminal of the Protective Circuit Module (PCM) melts and then hardens so that the terminal of the PTC device is both electrically connected to the electrical terminal of the Protective Circuit Module (PCM) and is physically fixed thereto.
However, PTC devices are generally long with respect to the dimensions of a bare cell or PCM and both ends thereof in the length direction are formed as terminals in order to connect a PTC device to bare cells or Protective Circuit Modules (PCM's). Since only one terminal is disposed on the conductive layer of the electrical terminal of any one Protective Circuit Module (PCM), the original directions in which PTC devices are disposed may twist out of the designed orientation because of external forces during the manufacturing process or when the conductive layer melts in the high temperature region. This causes a problem in welding bare cells and the terminal as well as causes an external short-circuit since a portion of the PTC devices goes beyond the range of thickness of the bare cells.
Conventional PTC devices are connected to Protective Circuit Modules (PCM's) by soldering on surface mount devices (SMDs) using a surface mount technology (SMT). Although the SMT is used to mount PTC devices on SMDs by soldering, since one side of the PTC devices is fixed by a solder method but the other side thereof is not fixed by the solder method, PTC devices may sway or twist either during a mounting process or a subsequent process.